Temperature effects and photodecomposition in fluorescence spectrometry

Abstract

The fluorescence efficiency of many compounds is very sensitive to temperature variations and for accurate work, temperature regulation is necessary [1, 2]. Fluorescence yields and decay times usually decrease with increasing temperature due to enhancement of the probability for internal conversion and intersystem crossing to the triplet manifold. On the other hand, the rate of collisional quenching decreases as the viscosity of the medium is increased so that collisional quenching of fluorescence in liquid media is less serious as the temperature is lowered. (This generalization does not always hold if the solute has two or more excited states which are slightly different in energy. In a compound in which T₁ * lies just below S₁ * e.g. anthraquinone [3] intersystem crossing from S₁ * to T₁ * may be followed by thermal excitation of the triplet back to S₁ * — hence the fluorescence intensity will increase with temperature).